1. Field of the Invention
The present invention is related to a method and apparatus for the production of methanol and more specifically to a continuous method and apparatus using condensed carbonaceous raw materials such as coal, natural gas, (i.e.; methane) wood, municipal solid waste, other biomass and other carbonaceous material for such production.
2. Description of the Prior Art
Methanol, which was first discovered in the late 1600's, has found uses as a chemical feedstock, as well as an efficient fuel. Its earliest and largest use to date is as a feedstock in the production of formaldehyde. While in recent years such use has decreased, methanol has found increasing use in the production of such materials as acetic acid and methyl tert-butyl ether (MTBE--a gasoline additive). In addition, methanol is being used directly (with increasing demand) as a fuel in race cars, in farm equipment and, in some areas, as a general purpose automotive fuel.
As will be discussed further below, there are several commercially viable methods of producing methanol. While different feedstocks are used and various processing steps are involved in these methods, they all must produce or otherwise provide carbon monoxide and hydrogen in a molar ratio of 1 mole of CO to 2 moles of H.sub.2. These reactants are then reacted in a methanol synthesis reactor to produce methanol in accordance with the following exothermic reaction: EQU CO+2H.sub.2 .fwdarw.CH.sub.3 OH
The processes known in the art often also produce carbon dioxide which, if fed into the methanol synthesis reactor, results in a lower methanol yielding reaction which competes with the above reaction for the valuable hydrogen as follows: EQU CO.sub.2 +3H.sub.2 .fwdarw.CH.sub.3 OH+H.sub.2 O
The oldest method of producing methanol on a commercially significant scale was the destruction distillation of wood. However, this method is no longer practiced in the United States.
A current conventional source of methanol, which produces approximately ninety (90%) percent of the methanol used, is the conversion of natural gas to methanol. This process involves the catalyzed conversion or reforming of the natural gas with steam to a synthesis gas containing principally carbon monoxide and hydrogen which synthesis gas is subsequently converted to methanol in the presence of a second catalyst. Excess hydrogen is either vented or used as a fuel.
A second method of preparing methanol taught in the art uses condensed carbonaceous material such as fossil fuels, biomass, wood, paper, plastic and the like. This approach involves gasifying the condensed carbonaceous material with steam and oxygen at elevated pressure and temperature to produce hydrogen and carbon monoxide in approximately a 1:1 molar ratio. As discussed above, a 2:1 molar ratio of hydrogen to carbon monoxide is necessary for the production of methanol. In this process, that is accomplished by further reacting some of the carbon monoxide with steam to form the additional hydrogen required to produce methanol. This second step takes place in a shift reactor and also produces carbon dioxide. The gas from the shift reactor must be solvent washed or scrubbed to separate and remove the carbon dioxide, which is vented to the atmosphere, leaving a process gas containing mainly hydrogen and carbon monoxide in a molar ratio of approximately 2 to 1 for feeding to a catalytic methanol convertor, where methanol is produced. Excess gas is either used as fuel or is vented,
While this approach may use a broader class of feed material than the forst process described, it does not achieve high methanol yields per quantity of feedstock and has than desirable thermal and carbon condensed efficiency. Furthermore, the second method requires the shift reaction (an extra step) to produce H.sub.2 /CO in the 2:1 molar ratio as needed by the methanol synthesis reactor to maximize the production of methanol per unit of feedstock. In addition, this second process also produces carbon dioxide in large quantities which must be removed prior to entry of the shift reaction products into the methanol synthesis reactor to prevent reduction of the methanol yield. Furthermore, this process also requires pure oxygen for the gasifications reaction which is endothermic.
A more detailed discussion of the above processes can be found in Kirk-Othmer Encyclopedia of Chemical Technology, Vol. 15, pp 398-415, John Wiley & Sons (1978).
It is therefore an object of the present invention to provide an efficient method and apparatus for the production of methanol from condensed carbonaceous material.
It is another object of the present invention to provide a method and apparatus for the production of methanol which produces a higher yield of methanol per unit feedstock.
It is another object of the present invention to provide a method and apparatus for the production of methanol with a reduced mass and thermal loss.
It is still another object of the present invention to provide a method and apparatus for the production of methanol which does not require a shift reactor to produce hydrogen and carbon monoxide in a molar ratio of 2:1.
It is yet another object of the present invention to provide a method and apparatus for the production of methanol having reduced carbon dioxide emissions and which eliminates the need for carbon dioxide removal.
It is still another object of the present invention to provide a method and apparatus for the production of methanol which eliminates the need for oxygen.
It is yet another object of the present invention to provide a method and apparatus for the production of methanol which gives a higher yield of methanol per unit of feedstock and has a higher thermal and carbon conversion effeciency than the conventional processes.
The above and other objects and advantages of the present invention will become apparent from the following specification read in conjunction with the annexed drawings.